Torque sensing tool

ABSTRACT

A torque applying tool such as a nutrunner or torque wrench incorporates torque sensors responsive to strain in a shaft mounting an output square drive head the strain being measured as it exists immediately adjacent the drive head. The shaft is a hollow quill shaft an outer diameter of which is splined to receive a torque drive input at a location axially spaced from the drive head. A central shaft extends from the drive head centrally up the quill shaft and a flexible cantilever beam is mounted between a cranked end of the central shaft as it extends out of the quill shaft and the corresponding end of the quill shaft. One or more strain sensing transducers, preferably S.A.W. devices, are mounted on the cantilever beam to detect flexure of the beam, and the resulting output signal is passed through an inductive or capacitive coupling for transmission to a CPU and display.

FIELD OF THE INVENTION

The invention relates to torque applying tools, such as nutrunners andtorque wrenches, incorporating torque sensors.

BACKGROUND INFORMATION

In torque applying tools such as nutrunners and torque wrenches it isdesirable to incorporate a display or printout indicating the torqueapplied by the tool during use of the tool to tighten threadedfasteners. In assembly line production a tool may be set to tightenbolts to a predetermined torque setting, for example. It is desirable tohave a visual display or print-out of the torque actually applied, forquality control and safety purposes. For that reason, torque wrenchesand nutrunners often have associated displays of sensed applied torque.

Often however the sensed torque is little more than approximation orestimate of the torque actually applied to the bolt or other threadedfastener. It has never been possible to sense the torque at the drivehead itself of the tool due to space limitations at the drive head. Thetorque sensors or strain gauges necessary to measure the applied torquehave typically been spaced along the side handle of a torque wrench oralong the drive train between a motor and a bevel drive gear of anutrunner. It has generally been accepted that errors between the torqueas measured at a point somewhat distant from the drive head and thetorque exerted by the drive head are small in comparison with thetorques being imposed; and are inevitable and unavoidable. The errorsmay arise, for example, from friction between the meshing teeth of thebevel gears of a nutrunner, or may take the form of cyclical errorsarising from inaccuracies In the grinding of those teeth or in thebearings for the drive head. Nevertheless those errors do exist andlimit the accuracy of torque sensing in known tools.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a torque applying toolincorporating a torque sensor which more accurately senses torque at thedrive head of the tool.

The invention provides a torque applying tool comprising a torque wrenchor nutrunner having handle means and a drive head for torque output;wherein the drive head is located at one end of a hollow quill shaft anouter diameter of which is splined to receive a torque drive input at alocation axially spaced from the drive head; a central shaft extendsfrom the drive head up the hollow centre of the quill shaft; and theends of the hollow quill shaft and the central shaft remote from thedrive head mount opposite ends of a flexible cantilever beam on a faceof which or on opposed faces of which are mounted one or more strainsensing transducers the output or outputs of whichrepresentsensed torqueapplied by the drive head.

The transducers, preferably two in number on opposed faces of thecantilever beam, are preferably Surface Acoustic Wave (S.A.W.)transducers which are capable of providing accurate digital outputs evenat low strain levels. S.A.W. transducers are available with a quartzsubstrate, with high Q factors which means that they can store andre-store energy efficiently.

In a nutrunner the drive head rotates relative to the handle means. In atorque wrench with a ratchet handle the drive head may similarly rotaterelative to the handle means. In either case the one or more straintransducers similarly rotate relative to the handle means. The outputsof such rotary strain sensing transducers are preferably transmitted toa non-rotary element in the handle via slip rings or across an air gap.For example the transducer outputs may be transmitted by a highfrequency, preferably radio frequency, coupling between a rotarycoupling element connected to the drive head and a non-rotary couplingelement connected to the handle means. The coupling elements may forexample be the elements of an inductive or a capacitive coupling. Theoutput from the transducer or transducers may then be taken from thenon-rotary coupling element either by a wired connection to a processorand display or via a patch antenna carried by the handle means, whichtransmits the output to a remote receiver, processor and display.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an axial section through a working head of a known nutrunnerincorporating a torque sensor;

FIG. 2 is a schematic assembly view of a complete nutrunner according tothe invention together with an associated CPU and visual display for thesensed torque;

FIG. 3 is an axial section through a part only of a working head of thenutrunner of FIG. 2;

FIG. 4 is an enlarged detail of the torque sensing portion of thenutrunner of FIG. 2;

FIG. 5 is a view from above in the direction of the arrow X of FIG. 2with the cover and both inductive elements removed; and

FIG. 6 is a view similar to that of FIG. 5 but with only the upper oneof the two inductive elements removed.

DETAILED DESCRIPTION

The drawings all relate to powered nutrunners in which an output squaredrive head is driven by a motor through a gearbox and bevel gear.However it will be understood that the invention is equally applicableto torque wrenches which have a similar output square drive headconnected, optionally through a ratchet mechanism, to a side arm handlethrough which torque is applied manually. In both cases the torque isapplied to a splined shaft which terminates in the output square drivehead.

Referring first to FIG. 1, a drive head 1 of a known powered nutrunnercomprises an output square drive head 2 mounted at one end of a splinedshaft 3. The shaft 3 is mounted on bearings, of which the upper bearing4 is shown. A bevel gear 5 is drivingly connected to the shaft 3 bycooperating splines 6 on the shaft and gear.

A second bevel gear 7 is a drive gear for the shaft 3 and drive head 2and is mounted on a drive shaft 8 which is arranged perpendicularly tothe shaft 3. The drive shaft 8 is mounted between bearings 9 and 10 andterminates in a hexagonal head 11 which in use receives a drive from amotor (not shown) which could for example be air or electric poweredthrough a gearbox (not shown) both of which are located within a sidehandle of the nutrunner.

A torque sensor is built into the known powered nutrunner of FIG. 1 andcomprises a strain gauge 12 mounted on the drive shaft 8 between thebearings 9 and 10. The strain in the drive shaft 8 sensed by the straingauge 12 is transmitted by wire or by a wireless link to a CPU anddisplay (not shown) where the measured strain is converted and displayedas a measure of the applied torque. The strain gauge 12 could be aconventional strain gauge or one the uses Surface Acoustic Wave (S.A.W.)technology.

The strain gauge 12 measures the strain at the drive shaft 8 between thebearings 9 and 10, and not at the output square drive head 2. Errors canoccur due to friction at the bearings 9 and 4, friction between thebevel gears and side loads exerted on the handle of the nutrunner inuse, and those errors cannot adequately be compensated in the nutrunnerof FIG. 1. The calculated and displayed torque is therefore never acompletely accurate indication of the torque exerted by the square drivehead 2.

FIGS. 2 to 6 illustrate a powered nutrunner according to the invention.FIG. 2 shows the nutrunner, indicated 20, in side view. The nutrunner 20has a motor portion 21, a gearbox portion 22 and a drive head portion 23all enclosed in a housing 24. The drive head portion 23 includes anoutput square drive head which is identical to that of FIG. 1 and whichhas therefore been given the same reference numeral 2.

Power to the electric motor contained in the motor portion 21 issupplied through a power cable 25. The motor is a high speed low torquemotor whose output is converted by the gearbox portion 22 to a low speedhigh torque drive to the output square drive head 2.

FIG. 2 also shows a cover 26 for a torque sensor assembly which isdescribed in detail below. A patch antenna (not shown) transmits torqueoutput signals to a CPU 27 which enables torque data to be displayed at28.

FIGS. 3 and 4 illustrate the connection of the torque sensors to thesquare drive head 2. The drive head 2 is formed or mounted on an end ofa quill shaft 30 which is externally splined at 6 to receive the inputdrive from a bevel gear 5. The spline connection 6 and the bevel gear 5are numbered with the same reference numerals as those used in FIG. 1 tosignify that the parts and functions are equivalent between the twodrawings.

The quill shaft 30 illustrated in FIG. 2 has a slightly reducedthickness wall at 30 a, to facilitate slight flexure of the quill shaftunder strain when the nutrunner applies torque to a rotary fastener inuse. Such a wall thickness reduction is not necessary however, as longas the quill shaft has an appropriate degree of flexibility. Torqueexerted between the bevel gear 5 and the output square drive head 2manifests itself as that slight flexure of the quill shaft 30 betweenthose two points. To measure that flexure a central shaft 31 is securedfast to the bottom. end of the quill shaft 30 immediately adjacent theoutput square drive head 2 and extends up through the hollow centre ofthe quill shaft and into the cover 26.

Within the cover 26 the top end of the quill shaft 30 opens out into acup portion 32 which mounts one end 33 of a flexible cantilever beam 34.The other end 35 of the cantilever beam 34 is gripped between fulcrumpoints 36 of a cranked end portion 37 of the central shaft31. Thefulcrum points 36 are not shown in FIGS. 3 and 4 but are illustrated inFIG. 5.

Secured to opposed outer faces of the flexible cantilever beam 34 are apair of strain gauges 38, one on each outer face of the beam. Analoguestrain gauges may be used, but the strain gauges 38 are preferablyS.A.W. devices which are highly accurate in measuring small strainreadings and have a digital output which assists the further processingof their output signals.

The outputs of the strain gauges 38 are fed to the respective tracks 39a and 39 b of a rotary coupling element 39 which is mounted on the cupportion 32. The rotary coupling element 39 transmits energy to anon-rotary coupling element 40 mounted on the inside of the cover 26. Inthe steady state, when the output square drive head 2 has stoppedrotating and the nut or other rotary fastener element being tightenedhas stopped rotating, the signals from the coupling element 39 wired tothe strain gauges38 are thus coupled to the coupling 40 stably mountedwithin the cover 26.

The output signal from the coupling element 40 is shown in FIGS. 3 and 4as issuing down wire leads41. From there, the signal may be hard-wiredto the CPU 27 (FIG. 2) or may be transmitted to the CPU through awireless connection which may be by an IR, radio wave or other suitablelink.

The strain gauges 38, although mounted at the end of the quill shaft 30remote from the output square drive 2, accurately reflect the angulardeflection in the quill shaft between the bevel gear 5 and the outputsquare drive. Distortion of the output reading (representing sensedtorque) by applied side loads on the nutrunner tool handle is reduced toa minimum, as any side load applied to the quill shaft is also appliedto the central shaft 31. The output reading of applied torque, displayedat the display 28, is therefore an accurate display of the torqueactually applied by the output drive head 2. Moreover thesignal-to-noise ratio of the output is extremely high when S.A.W.transducers are used as described, and the provision of S.A.W.transducers on opposite sides of the beam 34 with mutually differentfrequencies of for example 200 MHz and 201 MHz respectively providesexcellent signal separation with very little cross-talk.

1. A torque applying tool comprising a torque wrench or nutrunner havinghandle means and a drive head for torque output, and means for sensingthe output torque applied by the drive head; wherein the drive head islocated at one end of a hollow quill shaft an outer diameter of which issplined to receive a torque drive input from the handle at a locationaxially spaced from the drive head; a central shaft extends from thedrive head up the hollow center of the quill shaft; and the ends of thehollow quill shaft and the central shaft remote from the drive headmount opposite ends of a flexible cantilever beam on a face of which oron opposed faces of which are mounted one or more strain sensingtransducers the output or outputs of which represent sensed torqueapplied by the drive head.
 2. A tool according to claim 1, wherein thetool comprises two of the strain sensing transducers mounted on opposedfaces of the cantilever beam.
 3. A tool according to claim 1, whereinthe outputs of the one or more strain sensing transducers aretransmitted by a radio frequency coupling between a rotary couplingelement connected to the drive head and a non-rotary coupling element inthe handle means.
 4. A tool according to claim 3, wherein the outputsignal representing sensed torque applied by the drive head istransmitted from a patch antenna carried by the handle means andreceiving as input the output from the non-rotary coupling element.
 5. Atool according to claim 1, wherein each of the strain sensingtransducers is a surface acoustic wave transducer.
 6. A tool accordingto claim 1, wherein the tool is a nutrunner and torque drive input tothe hollow quill shaft is provided through a bevel gear splined to thequill shaft at the location axially spaced from the drive head.
 7. Atool according to claim 6, wherein motive power to the bevel gear isprovided from a motor through a gearbox and another cooperating bevelgear.
 8. A tool according to claim 1, wherein the tool is a torquewrench and torque drive input to the hollow quill shaft is providedthrough the handle means splined to the quill shaft at the locationaxially spaced from the drive head.
 9. A torque applying tool comprisinga torque wrench or nutrunner having handle means and a drive head fortorque output, and means for sensing the output torque applied by thedrive head; wherein the drive head is located at one end of a hollowquill shaft an outer diameter of which is splined to receive a torquedrive input from the handle at a location axially spaced from the drivehead; a central shaft extends from the drive head up the hollow centreof the quill shaft; wherein the ends of the hollow quill shaft and thecentral shaft remote from the drive head mount opposite ends of aflexible cantilever beam on a face of which or on opposed faces of whichare mounted one or more strain sensing transducers the output or outputsof which represent sensed torque applied by the drive head; and theoutputs of the one or more strain sensing transducers are transmitted toa non-rotary element in the handle means via slip rings or across an airgap.
 10. A tool according to claim 9, wherein the outputs of the one ormore strain sensing transducers are transmitted by a radio frequencycoupling between a rotary coupling element connected to the drive headand the non-rotary coupling element in the handle means.
 11. A toolaccording to claim 9, wherein each of the strain sensing transducers isa surface acoustic wave transducer.
 12. A tool according to claim 9,wherein the output signal representing sensed torque applied by thedrive head is transmitted from a patch antenna carried by the handlemeans and receiving as input the output from the non-rotary couplingelement.
 13. A tool according to claim 9, wherein the tool is anutrunner and torque drive input to the hollow quill shaft is providedthrough a bevel gear splined to the quill shaft at the location axiallyspaced from the drive head.
 14. A tool according to claim 13, whereinmotive power to the bevel gear is provided from a motor through agearbox and another cooperating bevel gear.
 15. A tool according toclaim 9, wherein the tool is a torque wrench and torque drive input tothe hollow quill shaft is provided through the handle means splined tothe quill shaft at the location axially spaced from the drive head. 16.A torque applying tool comprising a torque wrench or nutrunner havinghandle means and a drive head for torque output, and means for sensingthe output torque applied by the drive head; wherein the drive head islocated at one end of a hollow quill shaft an outer diameter of which issplined to receive a torque drive input from the handle at a locationaxially spaced from the drive head; a central shaft extends from thedrive head up the hollow centre of the quill shaft; wherein the ends ofthe hollow quill shaft and the central shaft remote from the drive headmount opposite ends of a flexible cantilever beam on a face of which oron opposed faces of which are mounted one or more strain sensingtransducers the output or outputs of which represent sensed torqueapplied by the drive head; wherein the outputs of the one or more strainsensing transducers are transmitted by a radio frequency inductivecoupling between a rotary first induction coupling element connected tothe drive head and a non-rotary second induction coupling element in thehandle means; and the output signal representing sensed torque appliedby the drive head is transmitted from a patch antenna carried by thehandle means and receiving as input the output from the second inductionelement or set of induction elements.
 17. A tool according to claim 16,wherein each of the strain sensing transducers is a surface acousticwave transducer
 18. A tool according to claim 16, wherein the tool is anutrunner and torque drive input to the hollow quill shaft is providedthrough a bevel gear splined to the quill shaft at the location axiallyspaced from the drive head.
 19. A tool according to claim 16, whereinmotive power to the bevel gear is provided from a motor through agearbox and another cooperating bevel gear.
 20. A tool according toclaim 16, wherein the tool is a torque wrench and torque drive input tothe hollow quill shaft is provided through the handle means splined tothe quill shaft at the location axially spaced from the drive head.